One known phase shifter used in the microwave band is disclosed in Patent Document 1 below. According to this Patent Document, the output from a VOC is down-converted to a low-frequency signal, and the phase of the output from the VOC is controlled such that the phase difference between the low frequency signal and a phase-controlled reference signal having the same frequency as that of the low frequency signal becomes zero. In this manner, the phase in the microwave range can be controlled using the phase of the low-frequency signal. In the microwave range, the phase of a microwave can be electrically controlled by electrically controlling the capacity or dielectric constant of a strip line.
Meanwhile, Patent Document 2 and Non Patent Document 1 disclose a known high-sensitivity wave detector using a microstructure. In such a wave detector, one end of a carbon nanotube extending straight is fixed to a negative electrode as a fixed end. The other end serves as a free end. The free end faces a planar positive electrode, and a DC bias voltage is applied between the positive electrode and the negative electrode. In this device, a tunneling current due to field emission of electrons flows from the free end of the carbon nanotube toward the positive electrode, and the magnitude of the current varies according to the distance between the free end of the carbon nanotube and the positive electrode. The cantilevered carbon nanotube with one end fixed has a mechanical natural resonance frequency. When the frequency of an incoming wave coincides with the resonance frequency, the carbon nanotube vibrates significantly in an arc about the fixed end. If the resonance frequency can be changed, the device can be tuned to a specific radio wave.
The tip of the carbon nanotube is charged with electric charges as a result of application of the DC bias voltage. Under the assumption that the carbon nanotube extends from its fixed end along a straight line (serving as a center axis), the electric charges at the tip receive forces due to the electric field of an incoming wave. These forces are proportional to the magnitude of a component of the electric field of the incoming wave which component is normal to the center axis of the carbon nanotube (this component is hereinafter referred to as a “normal component”). When an incoming wave is present, the carbon nanotube in a tuned state vibrates significantly about the center axis with the same amplitude on both sides. This vibration causes the distance between the free end of the carbon nanotube and the positive electrode to vibrate at a frequency twice the frequency of the incoming radio wave, and the amplitude of this vibration is proportional to the normal component of the electric field of the incoming wave. In this case, the tunneling current also vibrates at a frequency twice the frequency of the incoming wave, and the amplitude of this vibration is proportional to the normal component of the electric field of the incoming wave. In the device proposed in Patent Document 2 and Non-Patent Document 1, the above-described principle is used to detect a radio wave using only the carbon nanotube, the negative electrode, the positive electrode, and the DC bias power source.
Non-Patent Document 2 discloses a device having the structure described in Non-Patent Document 1 and further including an electrode parallel to the carbon nanotube. This electrode is applied with an AC voltage which, is DC-biased with a voltage V0, has a frequency twice the frequency of the incoming wave, and has an amplitude Vp. In this device, the amplitude of the vibration of the carbon nanotube can be changed by adjusting the DC bias voltage V0 and the value of the amplitude Vp, i.e., gain can be controlled.